1. Field of the Invention
The present invention is a device for resuspending liquid contents of microcentrifuge tubes by simulating the technique of finger vortexing.
Since the advent of culturing microorganisms, technology has been developed to mix liquid suspensions in a controlled and rhythmic pattern. Circular shakers continuously swirl samples in a circular motion, while reciprocating shakers mix samples with a back and forth motion. Motor-driven propellers, as well as forced aeration, serve to mix samples by homogenizing the contents with direct physical agitation.
A similar technology has been developed for mixing smaller sample volumes, e.g., 0.5-1.5 ml microcentrifuge tubes typically used for overnight bacterial plasmid preparations. The technology is simply a miniaturized version of the larger capacity shakers; the same basic circular motion used to mix large volume samples is used to mix small volume samples. These devises are maladapted to mixing small volumes of cells and solutions used in molecular and chemical analyses.
One way to mix and resuspend samples is "finger vortexing" (see FIG. 1). The action relies on a steadily held neck region of the tube while quickly, but gently, moving the bottom of the tube. The pull-and-release action moves the tube back to its original position. The action of finger vortexing is best described using a three dimensional model with a three axes, x-y-z, coordinate system (see FIG. 2). Herein described is an invention that simulates, upon multiple microsample tubes, this finger vortexing action.
2. Description of the Related Art
Biochemical and molecular techniques frequently require manipulations of samples with small volumes. These samples are often contained within microcentrifuge tubes, e.g., microliter volumes of chemical reactions at elevated temperatures (25-45.degree. C.) or milliliter volumes of cell cultures incubated overnight for plasmid production. Apparatuses abound for handling small volumes, but mixing and incubating these samples are usually performed in large incubators or heated rooms within which are housed large circular shakers (onto which many researchers "lash" on or attach their microcentrifuge tube racks with tape or rubber bands). Smaller reciprocating shakers that can accommodate at least 24 microcentrifuge tubes are available but expensive. Heated models of the smaller reciprocating shakers are even more expensive.
These conventional products utilize the same rapid circular motion of the full-sized design, except in a miniaturized form. Due to the disproportionate increase in surface area to volume when converting from large flasks to microcentrifuge tube-sized samples, greater sheer forces will be produced along the walls of the tubes during high-speed circular motion, e.g., 2500 rpm. Unforeseen elements involved when using reciprocating technology potentially add unknown and complicating factors to the growth of microorganisms or reactions of chemicals contained in small volumes in vitro. As the trend for miniaturizing continues in biology, there is a greater demand for better and more efficient ways to mix small volume samples with a smoother and more size appropriate strategy.
One of the most efficient and simplest ways scientists are taught for mixing test-tube samples is the technique of finger vortexing the bottom of the tubes at regular intervals. When many microcentrifuge tubes require gentle and rhythmic thumping, a new design (with many more fingers) is necessary. This simple way of resuspending solutions in tubes eliminates the sheer forces produced, as in the aforementioned reciprocating shakers, which may damage vesicles or sheer-sensitive cells.
However, a recent technology search failed to uncover any microcentrifuge tube mixers which were based on the principle of finger vortexing. For example, U.S. Pat. No. 5,215,376 (Schulte et al.); U.S. Pat. No. 4,895,453 (Devlin et al.); U.S. Pat. No. 4,848,917 (Benin et al.); U.S. Pat. No. 4,747,693 (Kahl); U.S. Pat. No. 4,305,668 (Bilbrey); U.S. Pat. No. 4,118,801 (Kraft et al.); U.S. Pat. No. 4,057,148 (Meyer et al.); U.S. Pat. No. 4,004,883 (Meyer et al.); U.S. Pat. No. 3,850,580 (Moore et al.); and U.S. Pat. No. 3,401,034 (Moore) all describe mixers which use circular or orbital motion to swirl and mix tube contents. The orbital path is generated by an eccentric drive.
U.S. Pat. No. 3,159,384 (J. E. Davis, 1964) discloses an agitator which does not impart circular motion directly to the tubes. Instead, in conjunction with the unit's eccentric drive, a reciprocating agitation mechanism is incorporated "to break up particulate matter adhered to the walls of the tube of the flask."
Thus, none of the aforementioned patents directly or specifically addresses the issue of resuspending contents of microcentrifuge tubes based on the principle of finger vortexing.
The present invention is a multiple microcentrifuge tube mixer/incubator designed to accommodate small volume samples. The innovation lies in the low-intensity mechanism that pulls-and-releases of, for example, 1-1000 tubes at a time in a slow and rhythmic pattern. Thus, the present invention is an apparatus for mechanically finger vortexing micro-centrifuge tubes.